Get over 500 total head shots in Multiplayer mode to unlock the Sniper Rifle.

Warfighter mode

Successfully complete the game on any difficulty setting to unlock the Warfighter difficulty setting.

Slip and slide

While running, quickly click the Left Analog-stick to slide along the ground or click and hold the Left Analog-stick to do a sort of belly flop and slide on your stomach.

Get on roof in Treasury level

In the Treasury level, it is possible to get up on the roof of the treasury. Have your pistol or grenade equipped in order to run faster. Run directly at the back door and dive into it; do this by running and quickly clicking the Right Analog-stick. Make sure your head hits the door and you should teleport to the roof. This also works on the level with the wall. You can teleport up into the rooms on the ends of the wall. Note: This may require some practice and should work with any building with an overhanging ledge that you can dive under.

Achievements

Accomplish the indicated achievement to get the corresponding number of Gamerscore points: